Wavelength-division-multiplexing (WDM) affords bidirectional communications and multiple channel communications over a single optical fiber link in a lightwave communication system. For an exemplary bidirectional system between two end stations, each station transmits at an assigned wavelength. See, for example, Elect. Lett., Vol. 21, No. 20, pp. 928-9 (1985). In order to receive signals from the remote end station, the receiver must operate at a wavelength different from the assigned transmitter wavelength. Separate waveguides connect the transmitter and the receiver to the optical fiber. Wavelength blocking filters and wavelength selective or routing couplers have been used to direct lightwave signals from the optical fiber to the receiver and from transmitter to the optical fiber.
By employing WDM, it is possible to design around crosstalk between signals of significantly differing strengths, namely, the high optical power signal from the transmitter and the relatively low optical power signal to the receiver. Unfortunately, receiver interference is caused by near end crosstalk from Fresnel reflections and Rayleigh backscattering of lightwave signals from the optical fiber. Receiver interference degrades receiver sensitivity and impairs WDM system performance. While WDM techniques offer the potential for bidirectional transmission on a single optical fiber, it is clear that realization of a WDM system is costly and architecturally complex. Both cost and complexity combine to make these techniques unattractive for communication systems having a large number of stations such as local area networks and "fiber to the home" applications.